The present invention relates to a method for reactivating a cylinder of a multicylinder internal combustion engine after interruption of the electromechanical actuation of at least one charge cycle valve, or after interruption of the combustion in at least one cylinder for a plurality of working cycles.
Internal combustion engines having charge cycle valves which are electromechanically actuated are well known. In contrast to camshaft-actuated valves, these valves are actuated as a function of the rotational position of the crankshaft in order to be opened and closed by a control unit. Accordingly, there is no fixed mechanical coupling to the crankshaft.
Charge cycle valves are disclosed, for example, in the German laid-open publication EP 0 724 067 A1. Said charge cycle valves each have a position of rest which lies between a closed position and an open position and from which they can be electromagnetically deflected. In the position of rest, the charge cycle valve is in a half opened position. When the electromechanically actuated valve is operated in the internal combustion engine, one or more electromechanically actuated valves may temporarily fail. When there is such a failure, the valve moves automatically into the half opened position of the position of rest. In order to prevent fuel which is then injected and not burnt in the cylinder from escaping into the exhaust gas tract and causing increased emissions or damaging the exhaust gas after-treatment system, the supply of fuel to this cylinder is interrupted immediately when the failure of the valve is detected. According to EP 0 724 067 A1, it is known in such a case to immediately close the electromechanically actuated charge cycle valve and then reactivate it again.
The German patent reference, DE 196 06 585 A1, discloses that switched-off charge cycle valves are switched on again and the respective cylinders are operated with corresponding corrected operating parameters during a transition phase. Here, the charge cycle valves are operated by camshafts and switched on and off hydraulically. In the transition phase, the internal combustion engine is operated with a slightly enriched mixture and the cylinders which are reactivated again are temporarily supplied with a larger quantity of fuel. It has become apparent that even with a fully functionally capable electromechanical drive, failure occurs again shortly after the resumption of the actuation of the charge cycle valve.
This can also be detected after a scheduled interruption of the combustion in at least one cylinder as is performed when there is an over-run fuel cut-off, in particular if a high load of the internal combustion engine is required after an over-run fuel cut-off.
The object of the present invention is therefore to provide a method for reactivating a cylinder of a multicylinder internal combustion engine with electromechanically actuated charge cycle valves after an interruption of the actuation of at least one charge cycle valve or after an interruption of the combustion in at least one cylinder with which the renewed operation of the cylinder can be initiated in a fail-safe fashion.
The aforesaid object is achieved by means of the present invention which is based on the recognition that, because a charge cycle valve has not been actuated and, for example, was in the position of rest, and/or no combustion has taken place, the combustion space is cooled to a greater or lesser extent as a function of the time for which the cylinder was not in operation. This cooling occurs primarily as a result of relatively cold air or exhaust gas being xe2x80x9cpumpedxe2x80x9d by the reciprocating movement of the piston. If the same control parameters (for example quantity of fuel, valve control times, ignition time or injection time, etc.) are selected for the reactivation of the cylinder of a spark emission internal combustion engine, or diesel internal combustion engine as in the other cylinders which have continued to be operated, severe cyclical fluctuations of the combustions, or even combustion misfires, occur in this cylinder when the non-operated cylinder is reactivated. In particular, the reduced combustion chamber temperature has negative effects on the burning rate and a significantly prolonged combustion in which the center of gravity of the combustion is not located, as is customary, 8 to 12xc2x0 CA, but rather approximately 30 to 50xc2x0 after the top dead center. In addition to this prolongation, there is often an increased proportion of fresh fuel mixture in the cylinder which would actually require a greater mass of fuel for the actuation.
The consequence of these circumstances are, that at the time at which the outlet valve is intended to open, the pressure in the combustion chamber is significantly higher in comparison to the other cylinders. Accordingly, the electromechanical actuation of the outlet valve must occur counter to a very large force. If this force is so large that the electromechanical actuation cannot move the charge cycle valve into the open position, there is a failure of the electromechanical actuation.
For this reason, the present invention provides that, when the cylinder is reactivated after interruption of the actuation of a charge cycle valve or the combustion, the cylinder is operated with different control parameters than the other cylinders. In this case, the load under which this cylinder is operated must not exceed a certain load threshold. As a result, the pressure in the combustion space at the time at which the outlet valve is to open is not increased so greatly despite prolonged combustion, and a failure of the electromechanical actuation of the charge cycle valve is avoided.
Hence, before the cylinder is reactivated, the cylinder is first operated for at least one cycle with full load control times, but no fuel is injected and no ignition is performed here. This ensures that there is predominantly air in the cylinder. Otherwise, this cannot generally be assumed since if, for example, the operation of the outlet valve has been interrupted, not only fresh mixture or fresh air but also exhaust gas is sucked in through the half open outlet valve when expansion occurs.